I have a category with subcategories, and I want to have the subcategory visible from the beginning, when the user opens the category selector.

Currently, the user has to click the arrow next to the parent category to expand it and have access to the subcategory when choosing categories. This needs to be auto-expanded, as soon as the user opens the category selection when creating a new product.

This attempt works. But in order to replace the old category selector, you have to add <field name="category_ids"> <argument name="data" xsi:type="array"> <item name="disabled" xsi:type="boolean">true</item> </argument> </field> and you have to change the value of dataScope from category_id to category_ids, else the values won't be saved.
– DorniApr 24 at 5:28